Pyloric stenosis in the stomach, illustration. The opening from the stomach to the duodenum (the first part of the small intestine) is called the pylorus. Abnormal narrowing (stenosis) of this area is called pyloric stenosis (shown in inset). This is a condition that mostly affects babies, and results in projectile vomiting. Atropine can be used to treat the condition, but surgery is often needed in a procedure known as a pyloromyotomy.